Ineos shutdown the plant this week in spite of the union calling off a planned 48-hour strike over the treatment of a convenor because Unite refused to guarantee there would be no more strikes this winter.

It then bypassed the union to put its survival plan directly to workers, while Unite urged employees not to co-operate with the firm’s demand for a Yes or No answer by Monday.

With the war of words escalating, Mr Salmond used his conference speech to attack both sides for issuing press releases that were “not helpful”, but noted that both sides said Grangemouth had a “great future”.

He pleaded with them to co-operate and negotiate before raising his voice, almost to the point of shouting, to say: “Scotland believes and Scotland expects that Grangemouth as an industrial facility has a great future.”

There was little immediate sign that either side was listening, as Unite accused Ineos of “blackmailing” the 1,400 workers to accept new terms, and of holding the UK and Scottish governments to ransom.

Michael Connarty, the local Labour MP, went further, accusing the management of being in collusion with the UK Government to shut down the petrochemical plant on the sprawling site.

He said: “It is quite clear that they are playing hard ball. They are saying if people don’t accept the survival plan then we would shut the chemicals and you could have up to 800 redundancies.

“They have gone to a cold shutdown for the first time I have ever been associated with the town to basically force the workforce into a situation where they will cut their own throats to allow the company to make profits.”

Meanwhile, Pat Rafferty, Unite’s regional officer, said Ineos had effectively told workers they should accept its survival plan, which would involve an end to the final salary pension scheme and a three-year pay freeze, or expect the site to close.

He said the company should not be allowed to get away with “playing Russian roulette” with the Scottish economy.

“We need the First Minister to be pushing the company to sit down in a reasonable, dignified fashion, and stop the gunboat diplomacy and the threatening attitude and approach the company is taking,” added Mr Rafferty.

“Both governments, Westminster and the Scottish Government, should be calling for the plants to get restarted. Right now you have got an individual who owns Ineos, in the shape of Jim Ratcliffe, who has a stranglehold on a key driver of the Scottish economy.”

Meanwhile, Calum MacLean, Ineos chairman, said yesterday was “D-Day for Grangemouth”, adding: “The shareholders have expressed extreme concern that the industrial action over recent days has cost the site £20 million at a time when losses are already £10 million per month. The site cannot afford this, hence the urgent need for employees to decide to support the company.

"We are going to give our employees a few days over the weekend to reflect on our proposals and then get their feedback. This feedback will be critical in influencing the shareholders in their decisions about what to do next."

The dispute centres around Stephen Deans, a union convenor who was embroiled in the dispute between Ed Miliband and Unite over the selection of a Labour candidate in Falkirk.

The party cleared Unite after an investigation into allegations of rigging the selection, but Mr Deans, chairman of the constituency Labour Party, still faces an internal inquiry.

Ineos said it would receive a report on the affair on Friday. It is understood the inquiry will look at phone and email records to determine whether he was working on the selection issue on company time.